Method for Processing Surface of Light-Transmitting Glass and Light-Transmitting Glass Processed by said Method

ABSTRACT

To impart antiglare properties without reducing the amount of transmitted light, a method for processing a surface of light-transmitting-glass according to the present invention comprises a blasting step of ejecting abrasive grains with particle sizes of #800 to #3000 (average particle diameter 14 μm to 4 μm) such as WA (white alundum: high-purity alumina) having higher hardness than that of the glass onto a light-receiving surface of the glass having light-transmitting property to be processed for forming indentations and protrusions in the light-receiving surface of the glass, and after the blasting step, a hydrofluoric acid treatment step of immersing the light-receiving surface of the glass into a hydrofluoric acid solution in 10% to 20% concentration for 30 to 600 seconds thereby increase a height (amplitude) of indentations and protrusions of the surface of light-transmitting-glass.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for processing a surface oflight-transmitting-glass and to light-transmitting glass subjected tosurface processing with the method, and more particularly relates to asurface processing method for suppressing the occurrence of specularreflections at the surface of light-transmitting glass and tolight-transmitting glass processed by the said method, in other wordsthe said glass subjected to surface processing with the method.

2. Description of the Prior Art

At present, there is continuously increasing concern from society aboutenvironmental problems, and the use of energy referred to as “naturalenergy” or “renewable energy” such as hydroelectric power, wind power,geothermal power, wave power, and sunlight which have a lowenvironmental load is attracting interest.

As part of the use of such natural energy, photovoltaic power generationso called solar power generation in which power generation is performedby using solar energy is extensively used today, and photovoltaicmodules used in photovoltaic power generation are becoming morewidespread.

These photovoltaic modules have a construction in which a requirednumber of photovoltaic cells are connected in series or in parallel andarranged side-by-side then covered by a cover glass such as temperedglass, to form a package.

Accordingly, in cases where the cover glass has a flat surface,unpleasant glare is experienced due to reflected light that is reflectedat the surface getting into people's field of vision. Therefore, fromthe viewpoint of taking into consideration nearby residents, and fromthe viewpoint of safety in the vicinity of facilities such as ports,airports, roads, etc., photovoltaic modules endowed with antiglarespecifications by virtue of the cover glass being subjected to antiglaretreatment are becoming widespread.

As examples of such antiglare treatment for the cover glass of aphotovoltaic module, a number of technologies designed to reduce glarehave been proposed, such as a technology in which reflected light isdiffused by attaching a light-diffusing sheet having indentations andprotrusions formed thereon to the surface of a cover glass, therebyendowing the cover glass with antiglare properties (Japanese UnexaminedPatent Application Publication No. 2001-189479), a technology in whichdiffuse reflection is generated by forming indentations and protrusionsdirectly in the surface of a cover glass (Japanese Unexamined PatentApplication Publication No. HEI 11-298030), or a technology in which theconcentration of reflected light in a certain direction is prevented byforming multiple parallel grooves in the surface of a cover glass(Japanese Unexamined Patent Application Publication No. 2003-188399).

The cause of the glare experienced from a cover glass having a flatsurface that is not subjected to antiglare treatment is that thereflections occurring at the flat surface of the cover glass arespecular reflections as shown in FIG. 6A.

In other words, because specularly reflected light is reflected so as tobe concentrated in a certain direction in the form of a collimated beam,like sunlight, unpleasant glare is experienced due to the reflectedlight getting into someone's field of vision in a concentrated manner.

Therefore, in cases where a light-diffusing sheet having indentationsand protrusions formed in the surface thereof is bonded to the surfaceof a protective cover to diffuse the reflected light as disclosed in theabove-cited '479 patent document, or in cases where indentations andprotrusions or grooves are directly formed in the surface of aprotective cover to cause the reflected light to be diffused, asdisclosed in the above-cited '030 and '399 patent documents, because itis possible to avoid concentration of the reflected light in a certaindirection as shown in FIG. 6B, the glare experienced even in cases wherepart of the reflected light gets into the field of vision isconsiderably reduced, and as a result, it is possible to endow the coverglass with an effective antiglare effect by any of these methods.

However, in either case, namely, the case in which the light-diffusingsheet is bonded to the surface of the cover glass as described in theabove-cited '479 patent document, or the case in which indentations andprotrusions are directly formed in the surface of the cover glass asdisclosed in the '030 and '399 patent documents, with a photovoltaicmodule provided with a cover glass that is subjected to such antiglaretreatment, a decrease in electricity generating efficiency is found ascompared with a photovoltaic module provided with an untreated coverglass on which antiglare treatment is not performed.

Such a reduction in the amount of generated power is considered to occurbecause the amount of light incident on the photovoltaic cells providedin a layer underneath is reduced since the amount of light that passesthrough the cover glass is reduced by subjecting the cover glass to theabove-described antiglare treatment, and electricity generatingperformance which is an essential requirement of photovoltaic moduleshas been sacrificed at the expense of adding functions that take intoconsideration the nearby residents etc., namely, antiglare properties.

The above description has been given by taking the cover glass of aphotovoltaic module as an example of an article subjected to antiglaretreatment; however, the decrease in performance due to a reduction inthe amount of transmitted light as a result of performing the antiglaretreatment as described above is a problem that occurs not only with thecover glasses of photovoltaic modules, but also, in a similar manner,with light-transmitting glass subjected to antiglare treatment which isprovided in various other types of devices and apparatuses, for example,the cover glasses of water heaters using solar heat, transparent panelsused in greenhouses etc. for agricultural and horticultural uses, and soforth.

Thus, the present invention has been conceived to eliminate thedeficiencies in the conventional technologies described above, and anobject thereof is to provide a light-transmitting glass surfaceprocessing method that not only avoids a reduction in the amount oflight passing through light-transmitting glass, but conversely,increases it, while at the same time endowing the light-transmittingglass with antiglare properties, as well as to providelight-transmitting glass provided with antiglare properties and highlight-transmitting properties which are achieved by surface processingwith the method.

SUMMARY OF THE INVENTION

To achieve the above-described object, a method for processing a surfaceof light-transmitting-glass according to the present invention comprisesthe process including:

a blasting step of ejecting abrasive grains with particle sizes of #800to #3000 (average particle diameter 14 μm to 4 μm) such as WA (whitealundum: high-purity alumina) having higher hardness than that of theglass onto a light-receiving surface of the glass to be processed havinglight-transmitting property for forming indentations and protrusions inthe light-receiving surface of the glass; and

after the blasting step, a hydrofluoric acid treatment step of immersingthe light-receiving surface of the glass into a hydrofluoric acidsolution in 10% to 20% concentration for 30 to 600 seconds.

In the above method, the blasting step and the hydrofluoric acidtreatment step are performed so that, for the indentations andprotrusions formed in the light-receiving surface of the glass after thehydrofluoric acid treatment, in numerical value groups obtained bydividing the light-receiving surface of the glass into minute sectionseach of a prescribed size (for example, 0.2913 μm square sections) andmeasuring a height from a deepest portion to a highest portion invalleys of the indentations and protrusions in each section, thefraction of numerical values of 4 μm to 9 μm accounts for 90% or higher.

In analysis of a power spectrum obtained by Fourier transforming aroughness curve of the indentations and protrusions formed in thelight-receiving surface of the glass by the hydrofluoric acid treatment,the power spectrum of waveform components with wavelengths of 500 nm to1333 nm in the roughness curve after the hydrofluoric acid treatment isincreased relative to the roughness curve after the blasting and beforethe hydrofluoric acid treatment.

Light-transmitting glass according to the present invention is obtainedby blasting in which abrasive grains are ejected onto a light-receivingsurface of the glass having light-transmitting property, followed bysurface processing in which the glass is immersed in a hydrofluoric acidsolution,

wherein, for indentations and protrusions formed in the light-receivingsurface of the glass after immersion in the hydrofluoric acid solution,in numerical value groups obtained by dividing the light-receivingsurface of the glass into minute sections each of a prescribed size andmeasuring a height from a deepest portion to a highest portion invalleys of the indentations and protrusions in each section, thefraction of numerical values of 4 μm to 9 μm accounts for 90% or higher.

For the Light-transmitting glass, wherein in analysis of a powerspectrum obtained by Fourier transforming a roughness curve of thelight-receiving surface after immersion in the hydrofluoric acidsolution, the power spectrum at wavelengths of 500 nm to 1333 nm is 0.1μm² or more.

In the light-transmitting glass of the present invention subjected tosurface processing by the above-described method, higherlight-transmitting property than that of an untreated light-transmittingglass could be obtained, while at the same time imparting antiglareproperties by virtue of the indentations and protrusions formed in thesurface thereof.

As a result, when the light-transmitting glass of the present inventionis used as the cover glass of a photovoltaic module, for example, it ispossible to achieve an improvement in the electricity generatingperformance exceeding 3% at most, compared with a photovoltaic module onwhich an untreated cover glass is mounted. Therefore, it is possible toprovide a surface processing method and light-transmitting glass whichcan achieve both antiglare properties and an increase in the amount oftransmitted light.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of preferred embodiments thereofprovided in connection with the accompanying drawings in which:

FIG. 1 is a histogram showing the distributions of the measured heightsof individual sections obtained by dividing the light-receiving surfaceof light-transmitting glass into minute sections;

FIG. 2 shows roughness curves for the light-receiving surface oflight-transmitting glass in the untreated state, after blasting, andafter hydrofluoric acid treatment following the blasting step;

FIG. 3 is a diagram showing the relationship between wavelength and thepower spectrum obtained by Fourier transforming the roughness curvesafter blasting and after hydrofluoric acid treatment following theblasting step;

FIGS. 4A and 4B are diagrams for explaining the principle (predicted) ofchanges in the amount of transmitted light, where FIG. 4A is for thepresent invention, and FIG. 4B is for a Comparative Example;

FIG. 5 is a diagram for explaining the principle (predicted) ofconfinement of light transmitted through the cover glass; and

FIGS. 6A and 6B are diagrams for explaining reflection at thelight-receiving surface, where FIG. 6A is a diagram for explainingspecular reflection, and FIG. 6B is a diagram for explaining diffusereflection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method for processing the surface according to the present inventionincludes a blasting step of performing blasting on a light-receivingsurface of light-transmitting glass to be processed and a hydrofluoricacid treatment step of immersing the surface to be treated inhydrofluoric acid following the blasting step.

The light-transmitting glass to be processed for the method for surfaceprocessing according to the present invention is not particularlylimited, and besides ordinary glasses such as float glass, for example,glass that is subjected to a specific treatment like tempered glass maybe used. Moreover, with regard to the material, it is possible to usevarious types of known glasses as the processing target, such as sodalime glass, non-alkaline glass, aluminosilicate glass, quartz glass,borosilicate glass, bismuth-based glass, etc., and colored glasses mayalso be used.

As described above, blasting is performed on the light-receiving surfaceof the light-transmitting glass to be processed. The blasting isperformed by ejecting abrasive grains onto the light-receiving surfaceof the light-transmitting glass, causing collisions therewith, thusforming indentations and protrusions. By forming indentations andprotrusions in advance on the surface to be treated of thelight-transmitting glass in this way, the profile of the surfaceindentations and protrusions that are eventually formed by etching viathe hydrofluoric acid treatment to be described below is controlled.

The abrasive grains used in the blasting must exhibit a cutting abilityon the light-transmitting glass to be processed, and the abrasive grainshaving a higher hardness than the hardness of the glass to be processed(a New Mohs hardness of about 4.5 to 6.5) are used.

As such abrasive grains, it is possible to use ceramic-based abrasivegrains with grid-shapes, for example, alumina (New Mohs hardness: 12),silicon carbide (New Mohs hardness: 13), zircon (New Mohs hardness: 9),etc., and those whose particle sizes in the range #800 to #3000 (averageparticle diameter 14 μm to 4 μm) are used.

The abrasive grains can be ejected together with a compressed gas suchas compressed air by using a known blasting apparatus.

Blasting apparatuses that can be used include, among others, thedirect-pressure type in which abrasive grains introduced into apressurized tank are pressurized and ejected together with a compressedgas, and the suction type in which abrasive grains are merged with aflow of compressed gas and ejected, and either method may be used.

As for the ejecting conditions, the ejection can be performed in a rangeof conditions employed in general blast processing; for example,ejection can be performed with a ejecting pressure of 0.3 to 0.5 MPa andan ejecting time of about 500 to 600 s/m².

After the light-receiving surface of the light-transmitting glass issubjected to the above blasting step, it is immersed in a hydrofluoricacid solution to increase undulation (amplitude) in the indentations andprotrusions formed in the light-receiving surface by the blasting step.

A 10 to 20% solution is used as the hydrofluoric acid solution used inthe hydrofluoric acid treatment, and the treatment is performed for animmersion time in the range of 30 to 600 seconds.

1. Experiment for Confirming Treatment Conditions Purpose of Experiment

To confirm the blasting conditions and hydrofluoric acid treatmentconditions that can impart antiglare properties without reducing theamount of transmitted light.

Experimental Method

Surface processing was performed by performing blasting on thelight-receiving surface of a 90 mm×90 mm cover glass of a photovoltaicmodule by using a direct-pressure type blasting apparatus with aejecting pressure of 0.5 MPa and the nozzle distance set to 60 mm,followed by etching the light-receiving surface of the cover glass withhydrofluoric acid treatment, and the short-circuit current of thephotovoltaic module on which the surface-processed cover glass wasmounted was measured.

The blasting was performed on one cover glass (90 mm×90 mm) with twoprocessing times, namely, 6.72 seconds and 13.44 seconds, includingoverlapping portions (50 mm×90 mm).

During the above surface processing, the treatment conditions (1) to (5)below were varied:

(1) the particle size of the abrasive grains used in the blasting,(2) the processing time for the blasting,(3) the material of the abrasive grains used in the blasting,(4) the hydrogen fluoride concentration in the hydrofluoric acidtreatment, and(5) the immersion time in the hydrofluoric acid treatment;and how the short-circuit current changed was measured, in comparisonwith the short-circuit current of a photovoltaic module having anuntreated cover glass mounted thereto (Comparative Example 1).

In addition, as Comparative Examples 2 to 5, the short-circuit currentsof photovoltaic modules on which cover glasses subjected only toblasting but not to subsequent hydrofluoric acid treatment were mountedwere also measured.

Experimental Results

The results of the above-described experiments are shown in Tables 1 and2 below.

TABLE 1 Results of the experiment for confirming treatment conditions(the changes in blasting conditions) Blasting conditions Hydrofluoricacid Average treatment conditions Increase rate Particle ProcessingImmersion of short- Sample Particle Diameter time Concentration timecircuitcurrent NO. Material Size (#) (μm) (second) (%) (second) (%) Ex.1 WA 800 14.0 ± 1.0  6.72 10 60 102.55 Ex. 2 WA 1000 11.5 ± 1.0  6.72 1060 102.52 Ex. 3 WA 1200 9.5 ± 0.8 6.72 10 60 103.16 Ex. 4 WA 2000 6.7 ±0.6 6.72 10 60 102.45 Ex. 5 WA 2000 6.7 ± 0.6 13.44 10 60 102.45 Ex. 6GC 2000 6.7 ± 0.6 13.44 10 60 101.91 Ex. 7 WA 3000 4.0 ± 0.5 6.72 10 60102.06 Ex. 8 WA 3000 4.0 ± 0.5 13.44 10 60 101.82 Ex. 9 GC 3000 4.0 ±0.5 13.44 10 60 101.87 Comp. — — — — — — 100.00 Ex. 1 Comp. WA 800 14.0± 1.0  6.72 — — 99.48 Ex. 2 Comp. WA 1200 9.5 ± 0.8 6.72 — — 99.22 Ex. 3Comp. WA 2000 6.7 ± 0.6 6.72 — — 97.53 Ex. 4 Comp. WA 3000 4.0 ± 0.56.72 — — 94.93 Ex. 5

TABEL 2 Results of the test for confirming treatment conditions (thechanges in the hydrofluoric acid treatment conditions) Blastingconditions Hydrofluoric acid Average treatment conditions Increase rateSample Particle Processing Immersion of short- NO. Particle Diametertime Concentration time circuitcurrent NO. Material Size (#) (μm)(second) (%) (second) (%) Ex. 10 WA 1200 9.5 ± 0.8 6.72 10 30 101.59 Ex.11 WA 1200 9.5 ± 0.8 6.72 20 30 102.33 Ex. 12 WA 1200 9.5 ± 0.8 6.72 2060 101.66 Ex. 13 WA 1200 9.5 ± 0.8 6.72 10 120 103.02 Ex. 14 WA 1200 9.5± 0.8 6.72 10 180 102.77 Ex. 15 WA 1200 9.5 ± 0.8 6.72 10 300 102.51 Ex.16 WA 1200 9.5 ± 0.8 6.72 10 600 102.20 Comp. — — — — — — 100.00 Ex. 1

In the above results, when comparing the photovoltaic modules on whichonly the blasting was performed on the cover glass but subsequenthydrofluoric acid treatment was not performed (Comparative Examples 2 to5) with the photovoltaic module on which the untreated cover glass wasmounted (Comparative Example 1), it was confirmed that the short-circuitcurrents were reduced relative to that of the photovoltaic module onwhich the untreated cover glass was mounted (Comparative Example 1), inother words, that the amount of received light on the photovoltaic cellswas reduced.

Moreover, for such a reduction in short-circuit current, it wasconfirmed that the reduction factor increased as the size of theabrasive grains used decreased.

In contrast, for photovoltaic modules on which cover glasses processedby the method of the present invention were mounted (Examples 1 to 16),for all of them, the short-circuit currents were higher than that of thephotovoltaic module on which the untreated cover glass was mounted(Comparative Example 1), an increase in short-circuit current exceeding3% at most was confirmed. Therefore it was confirmed that the surfaceprocessing of the present invention afforded the advantageous effect ofincreasing the amount of received light on the photovoltaic cells. Thatis to say, the amount of light transmitted through the cover glass.

From the results in Table 1, in relation to the changes in the blastingconditions, by using WA abrasive grains (white alundum: alumina-basedabrasive grains) and GC abrasive grains (green carborundum: greensilicon carbide-based abrasive grains) which both have high hardness onthe cover glasses to be processed, no large difference was found in themeasured short-circuit currents due to differences in the materials ofthe abrasive grains (see Examples 5 and 6 and Examples 8 and 9).

Also, between the case where the blasting was performed only for 6.72seconds and the case where the blasting was performed for 13.44 seconds,that is to say, when the processing time was doubled, almost no changein the measured short-circuit currents was found (see Examples 4 and 5and Examples 7 and 8). Therefore, it was determined that a change in theblasting time has almost no effect on the performance after treatment.

On the other hand, regarding the particle size of the abrasive grains,the percentage increase in the short-circuit current peaked at 103.16%in the example using the abrasive grains with particle size of #1200(see Example 3), and a slight reduction in the percentage increase inthe short-circuit current was found for abrasive particle sizes largerthan or smaller than #1200; however, in the entire #800 to #3000 rangeof particle sizes specified in the present invention, increases in theshort-circuit currents compared with that of the photovoltaic module onwhich the untreated cover glass was mounted (Comparative Example 1) wereconfirmed.

Note that, the reflectance at an incident angle (relative to theperpendicular) of 5° at the untreated cover glass (ComparativeExample 1) measured by using a spectrophotometer was 11%, whereas forthe cover glasses of Examples 1 to 16 of the present invention, thereflectances at an incident angle (relative to the perpendicular) of 5°were all 8% or less. Thus it was also confirmed that the cover glassesof Examples 1 to 16 exhibited suitable antiglare properties.

2. Measurement and Evaluation of Surface Condition Purposes ofExperiment

To consider the reason (mechanism) by which the advantageous effect,namely, the increased amount of transmitted light is obtained, bymeasuring and evaluating the surface condition of the light-transmittingglass (cover glass of the photovoltaic module) subjected to surfaceprocessing with the method of the present invention.

Measurement and Evaluation Method

The measurements and evaluation below were conducted using a lasermicroscope (ultra-deep profile measuring microscope, “VK-8500”) andanalysis software (VK profile analysis software, “VK-H1A7”), bothmanufactured by Keyence Corporation.

(1) Measurement of Height Distribution of Indentations and Protrusions

An image obtained by acquiring the surface of the cover glass subjectedto the surface processing of the present invention with a lasermicroscope at 1000× magnification was divided into minute sections eachhaving a prescribed size (in this Example, 0.2913 μm square sectionscorresponding to one pixel of the image), a histogram was formed basedon measurement values obtained by measuring the height in each section(the height obtained with reference to the minimum height H_(min) whichis the deepest part in the valleys in the surface having indentationsand protrusions, which is defined as zero), and the surface conditionwas evaluated using the measured height distribution.

(2) Evaluation Based on Power Spectrum via Fourier Transformation

A power spectrum of the spatial frequency components (wavelengthcomponents) was determined by obtaining a roughness curve of the coverglass surface based on the image acquired by the laser microscope andperforming two-dimensional Fourier decomposition on the roughness curve.

Measurement Results (1) Height Distribution of Indentations andProtrusions

FIG. 1 shows histograms created on the basis of the measurement valuesobtained by measuring the height of each section with theabove-described method. From these histograms, it was confirmed thatindentations and protrusions of 4 to 9 μm accounted for 90% or more ofthe surface of the light-transmitting glass subjected to surfaceprocessing using the method of the present invention.

(2) Evaluation Based on Power Spectrum Obtained by FourierTransformation

FIG. 2 shows roughness curves of the untreated cover glass (ComparativeExample 1), the cover glass subjected to blasting using WA abrasivegrains with particle size of #2000 (Comparative Example 4), and thecover glass subjected to a 45-second treatment with 10% hydrofluoricacid after the blasting (Example 17).

FIG. 3 shows the results of determining the power spectrum of thespatial frequency components (wavelength components) by performingtwo-dimensional Fourier decomposition on the roughness curves in FIG. 2(note that, FIG. 3 has been simplified by limiting the wavelengthsdisplayed).

From the results shown in FIGS. 2 and 3 above, in comparison with thecover glass subjected only to the blasting (Comparative Example 4), forthe cover glass subjected to subsequent hydrofluoric acid treatment(Example 17), it was found that the depth of the indentation portions inthe indentations and protrusions formed by the blasting was increased bythe etching, and the height (amplitude) of the indentations andprotrusions thus increased.

In particular, as shown in FIG. 3, from the power spectrum obtained viaFourier transformation, such an increase in amplitude was found to beremarkable in the wavelength range of 500 to 1333 nm among the waveformcomponents constituting the roughness curve.

Discussion

From the above evaluation results of the surface condition, it isconsidered that the cover glass subjected to surface processing with themethod of the present invention exhibits an increase in the amount oftransmitted light due to the following mechanisms.

(1) Discussion Based on Height Distribution of Indentations andProtrusions

For the cover glass processed by the method of the present invention,among the heights of each section measured as described above, heightsof 4 to 9 μm accounted for 90% or more.

On the other hand, from the roughness curve, because the wavelengths ofthe waveform components became sufficiently small, namely, half or lessof the wave height for the surface of the cover glass after thehydrofluoric acid treatment, as schematically shown in FIG. 4A, theaspect ratio of the wave height (amplitude) h relative to wavelength λwas sufficiently large.

As shown in FIG. 4A and FIG. 4B, even if the cover glass has theindentations and protrusions formed on the light-receiving surfacethereof in both cases, with a cover glass in which the indentations andprotrusions have a wave height h that is smaller than the wavelength λas shown in FIG. 4B, almost all of the reflected light is nottransmitted through the cover glass and is therefore not used ingenerating electricity. However, with the structure in FIG. 4A with alarge aspect ratio of the wave height h to the wavelength λ of theindentations and protrusions, reflected light that is directed downwardas shown by the arrow in the figure, or towards the neighboring peakportion is easily generated, and it is thus possible to producereflected light that will pass through the cover glass. Accordingly, thereflected light that is not used for generating electricity in theconventional art can also be used for generating electricity, therebypresumably an increase in short-circuit current occurs.

In addition, as shown in FIG. 5, it is assumed that part of the lightthat is transmitted through the cover glass and reaches the solarbattery cells arranged in the layer therebelow is reflected at thesurface of the solar battery cells, and transmitted through the coverglass again, thus escapes to the outside. However, the light thatre-enters the cover glass in this way is incident on the inclinedsurface of the protrusion part at an angle θ which is an acute angle.The critical angle Io at the interface between the glass which has ahigh refractive index (a refractive index of 1.51 for soda lime glass)and the air which has a low refractive index (refractive index of 1) isgiven by

Io=arcsin(1/1.51)≈41.47°.

Therefore, most of such reflected light is totally reflected at theinterface between the glass and air so as to be confined withoutemerging from the cover glass, and therefore contributes to animprovement in electricity generating efficiency.

(2) Discussion Based on Fourier Transformation

Moreover, as shown in FIG. 3, from the power spectrum obtained by theFourier transformation, for the cover glass subjected to hydrofluoricacid treatment following the blasting step, an increase in the powerspectrum in the wavelength region 500 nm to 1333 nm was confirmed, andit was found that the waveform components at these wavelengths in theroughness curve increased.

Here, diffuse reflection of light occurs when the roughness of thereflecting surface is the same extent of magnitude as the wavelength ofthe light, or greater, and in sunlight, the region where the intensityis highest, that is to say, in the visible light region which is theregion that contributes most to electricity generation, is about 400 nmto 700 nm. Therefore, with the cover glass subjected to surfaceprocessing via the method of the present invention, in the roughnesscurve, wavelength components that are the same extent of magnitude as orsomewhat larger than the visible-light wavelengths are higher. Thus, itis considered that the cover glass is provided with the most appropriatesurface conditions for capturing sunlight via the above-describedprinciple.

3. Differences in Advantageous Effect by Processing Light-ReceivingSurface/Rear Surface Purpose of Experiment

To confirm what kind of difference occurs in terms of advantageouseffect between the cases where the light-receiving surface and the rearsurface of the cover glass are subjected to the surface processing ofthe present invention.

Expected Advantageous Effect and Experimental Method

In a photovoltaic module to which a cover glass subjected to surfaceprocessing with the method of the present invention is mounted, when itis assumed that an improvement in electricity generating efficiency isobtained by the principle described above, the surface processing of thepresent invention must be performed on the light-receiving surface ofthe light-transmitting glass, and when the surface processing of thepresent invention is performed on the rear surface of the cover glass(the surface on the opposite side from the light-receiving surface), itis expected either that the electricity generating efficiency does notchange or that the electricity generating efficiency decreases.

Therefore, cover glasses whose surface on the opposite side from thelight-receiving surface was subjected to surface processing by themethod of the present invention were mounted to a photovoltaic module,and the short-circuit currents were measured.

Experimental Results

Table 3 shows the surface processing conditions and the ratio ofshort-circuit currents relative to that of a photovoltaic moduleprovided with an untreated cover glass.

TABLE 3 Results of surface processing performed on the rear surface ofthe cover glasses Blasting conditions Hydrofluoric acid Averagetreatment conditions Increase rate Particle Processing Immersion ofshort- Sample Particle Diameter time Concentration time circuitcurrentNO. Material Size (#) (μm) (second) (%) (second) (%) Comp. — — — — — —100.00 Ex. 1 Comp. WA 1200 9.5 ± 0.8 6.72 20 45 99.66 Ex. 6 Comp. WA1000 11.5 ± 1.0  6.72 20 60 99.58 Ex. 7 Comp. WA 2000 6.7 ± 0.6 6.72 1060 98.08 Ex. 8 Comp. WA 2000 6.7 ± 0.6 6.72 10 90 98.03 Ex. 9

As is clear from the results in Table 3, when the method for surfaceprocessing according to the present invention was performed on the rearsurface of the cover glasses, it was confirmed that decreases in theshort-circuit currents in comparison with the case of the untreatedcover glass occurred.

From the above results, it was confirmed that the surface processing ofthe present invention is effective when performed on the light-receivingsurface of the light-transmitting glass.

Thus the broadest claims that follow are not directed to a machine thatis configured in a specific way. Instead, said broadest claims areintended to protect the heart or essence of this breakthrough invention.This invention is clearly new and useful. Moreover, it was not obviousto those of ordinary skill in the art at the time it was made, in viewof the prior art when considered as a whole.

Moreover, in view of the revolutionary nature of this invention, it isclearly a pioneering invention. As such, the claims that follow areentitled to very broad interpretation so as to protect the heart of thisinvention, as a matter of law.

It will thus be seen that the objects set forth above, and those madeapparent from the foregoing description, are efficiently attained andsince certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatters contained in the foregoing description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Now that the invention has been described;

What is claimed is:
 1. A method for processing a surface oflight-transmitting-glass comprising the process including: a blastingstep of ejecting abrasive grains with particle sizes of #800 to #3000having higher hardness than that of the glass onto a light-receivingsurface of the glass to be processed having light-transmitting propertyfor forming indentations and protrusions in the light-receiving surfaceof the glass; and after the blasting step, a hydrofluoric acid treatmentstep of immersing the light-receiving surface of the glass into ahydrofluoric acid solution in 10% to 20% concentration for 30 to 600seconds.
 2. The method according to claim 1, wherein the blasting stepand the hydrofluoric acid treatment step are performed so that, for theindentations and protrusions formed in the light-receiving surface ofthe glass after the hydrofluoric acid treatment, in numerical valuegroups obtained by dividing the light-receiving surface of the glassinto minute sections each of a prescribed size and measuring a heightfrom a deepest portion to a highest portion in valleys of theindentations and protrusions in each section, the fraction of numericalvalues of 4 μm to 9 μm accounts for 90% or higher.
 3. The methodaccording to claim 1, wherein in analysis of a power spectrum obtainedby Fourier transforming a roughness curve of the indentations andprotrusions formed in the light-receiving surface of the glass by thehydrofluoric acid treatment, the power spectrum of waveform componentswith wavelengths of 500 nm to 1333 nm in the roughness curve after thehydrofluoric acid treatment is increased relative to the roughness curveafter the blasting and before the hydrofluoric acid treatment.
 4. Themethod according to claim 2, wherein in analysis of a power spectrumobtained by Fourier transforming a roughness curve of the indentationsand protrusions formed in the light-receiving surface of the glass bythe hydrofluoric acid treatment, the power spectrum of waveformcomponents with wavelengths of 500 nm to 1333 nm in the roughness curveafter the hydrofluoric acid treatment is increased relative to theroughness curve after the blasting and before the hydrofluoric acidtreatment.
 5. Light-transmitting glass obtained by blasting in whichabrasive grains are ejected onto a light-receiving surface of the glasshaving light-transmitting property, followed by surface processing inwhich the glass is immersed in a hydrofluoric acid solution, wherein,for indentations and protrusions formed in the light-receiving surfaceof the glass after immersion in the hydrofluoric acid solution, innumerical value groups obtained by dividing the light-receiving surfaceof the glass into minute sections each of a prescribed size andmeasuring a height from a deepest portion to a highest portion invalleys of the indentations and protrusions in each section, thefraction of numerical values of 4 μm to 9 μm accounts for 90% or higher.6. The Light-transmitting glass according to claim 5, wherein inanalysis of a power spectrum obtained by Fourier transforming aroughness curve of the light-receiving surface of the glass afterimmersion in the hydrofluoric acid solution, the power spectrum atwavelengths of 500 nm to 1333 nm is 0.1 μm² or more.
 7. The methodaccording to claim 1, wherein the abrasive grains are white alundum orgreen carborundum abrasive grains.